In 1967 the American counterpart to a global motorcycle manufacturer requested the development of a vehicle that its dealers could sell during the winter season of slackening motorcycle sales. The result was the introduction of a three-wheeled all terrain vehicle (ATV) which debuted in 1970. This original ATV exhibited a tricycle geometry and employed a seven horsepower motorcycle engine to drive two rear twenty-two inch low pressure tires through a dual-range, four-speed gear box with an automatic clutch. The machines handled snow, mud and various slippery conditions which a motorcycle couldn't.
Further development optimized tire and chassis design. While then primarily a recreational device, farmers saw substantial utility in the ATV. In this regard, a farm tractor costs exponentially more than an ATV and a typical ATV utilized 8% of the fuel consumed by such a tractor. This multipurpose usage grew from about 30% of total usage to about 80% total usage in the current market. The other major ATV interest in the 1980s was racing everywhere from frozen lakes in the East to Western dessert to the dirt ovals of Middle America. Four-wheel machines were introduced in 1984 and were considered more versatile, particularly for utilitarian use. Inevitable accident statistics prompted the Consumer Product Safety Commission (CPSC) to mandate a four-wheel design. By 2001, the ATV industry was selling about 400,000 units per year.
Three basic types of ATVs have evolved to suit the needs of riders. These include: sport models referred to as “sport quads” which are used by high performers, for instance, in racing and to some extent by casual recreationists; utility models used for a wide range of work and recreation activities; and the smallest segment featuring a cargo box which are popular with farmers, ranchers and outfitters.
Utility models typically incorporate four-wheel drive and will weigh about 400-500 pounds. Sport quads incorporate two-wheel drive, somewhat expensive suspensions and more refined motors. Typically weighing about 370 pounds, these sport vehicles are quicker and more responsive than the utility models. Just as in essentially all forms of automotive racing, the talent of the driver is quite important. For instance, with two-wheel drive, when beginning a turn, a bit more throttle is employed and a slight “slide” of the rear wheels is developed. Thus the type of terrain on which the vehicles are driven has a high importance with respect to racing technique and generally varies from racing venue-to-venue.
As may be expected, sport quad racing also calls for a tuning of front end suspension which is characterized preferably with optimization for each track. For instance, the two front wheels are suspended from ball joints, in turn supported by upper and lower A-frames or control frames pivotally mounted to the chassis with rod end Heim joints. For a highest level of performance at each racing venue, experienced mechanics will adjust these suspensions for caster and camber. Caster is the angle between a vertical line and the ATV's steering axis when viewed from the side. It is measured in degrees and minutes. More caster (positive) generally gives more steering going into a turn, but less coming out. The opposite also obtains, less caster (negative) gives less steering going into a turn (initial steering), but more steering as the vehicle exits. Caster also may be adjusted to provide more stability on straightaway performance.
Camber, as seen from the front and rear of the ATV is the angle of the tires in relation to the ground. Tires that are perfectly perpendicular to the ground (90°) are said to be at “zero camber”. If the tops of the tires lean toward each other, the tires have negative camber, and if they lean out, the tires have positive camber.
While camber can be tuned by bolt and nut adjustment at the upper ball joint, caster cannot. Typically, caster is adjusted by removing the upper A-frame structure and making an adjustment at the rod end Heim joint. Unfortunately, that form of adjustment also affects camber. Accordingly, a substantial amount of talent is required for making a caster adjustment. Assuming adjustments have been made for given racing venue, the inherent structure of the front wheel suspensions are such that it is difficult to determine just what adjustment has been made as the vehicle is tuned for a next racing venue.